The fluorescent lamp is a widely utilized light source for general illumination applications, primarily because of its relatively low initial cost and its efficacy; i.e., its light output relative to its power input, usually expressed as lumens per watt (LPW). These fluorescent lamps are constructed in the wide variety of configurations and sizes. However, specific reference herein is made to compact fluorescent lamps. In this regard, refer to U.S. Pat. No. 4,560,357 assigned to the assignee of the present invention. Further reference will be made hereinafter to this U.S. patent.
There presently exists a number of different methods of jacketing a fluorescent lamp. One of the most rudimentary techniques is to simply envelope the light emitting tube or tubes in a transparent plastic or glass jacket. However, it has been found that this jacketing technique substantially reduces the light output of the lamp because the insulating properties of the jacket render the mercury vapor pressure inside the light emitting tubes too high. The high mercury vapor pressure substantially degrades the lamp efficiency.
Another method of jacketing a fluorescent lamp also envelops the light emitting tubes in a jacket. However, this method incorporates a mercury amalgam inside the light emitting tubes to lower the vapor pressure of the mercury during operation. A disadvantage of this method is that the amalgam is costly and difficult to incorporate in lamps. Additionally, the lamps require a longer warm-up time to full intensity than do standard lamps employing only mercury.
Another form of jacketed lamp is of the type disclosed in the aforementioned U.S. Pat. No. 4,560,357. In this method of making a fluorescent lamp, the inner lamp assembly, unfilled, and with its exhaust tubulation open, is mounted within the jacket or envelope. The envelope is then exhausted and filled with an arc generating and sustaining medium, and the envelope exhaust tubulation is sealed. The lamp is in operable condition because the arc generating and sustaining medium contained within the envelope penetrates the open inner lamp assembly tubing; which tubing is not hermetically sealed. One of the major disadvantages with this particular method of jacketing is that the exhaust step is too time consuming and/or alternatively requires some special techniques to rapidly heat the interior lamp components which, by virtue of the jacketing, are insulating from the outer environment.
In order to exhaust and fill a lamp of the type described in U.S. Pat. No. 4,560,357, the lamp is attached to an exhaust machine and the whole assembly is heated to speed-up the exhausting. However, because the inner lamp assembly has to be exhausted via the envelope, there is essentially a heat insulating environment therebetween that makes it quite difficult to conduct the heat properly to the inside lamp components and thus the step of exhausting is relatively slow. This requires that the lamp be left on the exhaust machine for too long a period of time.
Also, with the method described in U.S. Pat. No. 4.560.357, it is furthermore noted that there are additional tube constrictions, primarily in the form of the inner lamp assembly exhaust tubulation. These constrictions further slow the exhaust procedures.